This invention relates to a flux detector device and more particularly to an absolute incident extreme-ultraviolet radiation detector for in-situ monitoring.
In general lithography refers to processes for pattern transfer between various media. Projection lithography is a powerful and essential tool for microelectronics processing. FIG. 2 schematically depicts an apparatus for extreme-ultraviolet (EUV) lithography that comprises a radiation source 11, such as a synchrotron or a laser plasma source, that emits EUV radiation 12 into condenser 13 which in turn emits beam of light 14 that illuminates a portion of reticle or mask 15. The emerging patterned beam is introduced into the imaging optics 16 which projects an image of mask 15, shown mounted on mask stage 17, onto wafer 18 which is mounted on stage 19. Element 20, an x-y scanner, scans mask 15 and wafer 18 in such direction and at such relative speed as to accommodate the desired mask-to-image reduction.
Measuring and regulating the EUV radiation flux through the lithography system is critical to maximizing performance. Prior art techniques for measuring the flux typically employed devices with EUV-sensitive vacuum photodiodes, which were difficult to calibrate to an absolute standard. One reason is that the electronic work function of the surface on which the EUV radiation impinged was influenced by environmental conditions. This phenomenon is commonly known in the art to as xe2x80x9cband bending.xe2x80x9d For instance, surface contamination caused the work function to vary. Since the detector""s response changed with environmental conditions, it was necessary to continuously recalibrate the devices. The art is in need of a reliable, cost effective EUV radiation flux detector whose calibration.
The invention is based in part on the recognition that an EUV mirror based, absolute flux detector can be fabricated by embedding an integral EUV photodiode beneath a multilayer reflection stack. This detector exploits the fact that a multilayer reflection stack can be designed to selectively transmit a desired amount of radiation through the stack. For example, a 40 bi-layer molybdenum/silicon EUV multilayer reflection stack allows the transmission of approximately 0.7% of the mirror""s programmed peak wavelength through the stack. Since the intensities typically incident on the multilayer are quite high (approximately 109-1013 photons/cm2 shot), the signal generated on the photodiode after the 1:1000 attenuation will be quite high. Given that the detector has a multilayer reflection stack as the radiation incident surface, and that the diode detector does not respond to the photoelectric current originating from the surface of the detector (the way a vacuum photodiode operates), the response of this detector will not substantially change with time and/or environmental conditions.
In one embodiment, the invention is directed to an extreme ultraviolet (EUV) radiation flux detector that includes:
a photodiode with an EUV sensitive region;
a planarizing layer positioned on the EUV sensitive region of the photodiode; and
multilayer film positioned on the planarizing layer wherein the multilayer film is exposed to EUV radiation.